Solid ink or phase change ink printers conventionally receive ink in a solid form and convert the ink to a liquid form for jetting onto a receiving medium. The solid ink, either in pellet or ink stick form, is typically loaded into a feed channel of a printer. The solid ink is then delivered by gravity or mechanical force, or some combination of these forces, through the feed channel to a heater plate. The heater plate melts the solid ink into a liquid form and the liquid is conveyed to a printhead, which ejects the ink onto a receiving medium in accordance with a driving signal generated by a printhead controller.
The solid ink used in a solid ink printer can be any appropriate phase change ink that employs a suitable colorant, such as dye or a colored resin, and an ink carrier composition which is compatible with the colorant. The phase change ink of an appropriate composition can employ a carrier composition that utilizes a fatty-amide containing material, which may be any appropriate amide compound, such as typically a tetra-amide, and/or a tri-amide compound and/or a mono-amide compound or other suitable amides, and combinations thereof. Alternatively, the phase change ink can employ a urethane resin, a mixed urea/urethane resin and a monoamide, or any other carrier composition appropriate for jetting.
An appropriate colorant can be employed in the ink composition to achieve cyan, magenta, yellow and black colors suitable for ink jet CMYK subtractive color printing applications. These colored inks can be formed by using a single dye or a mixture of dyes. For example, magenta can be obtained by using a mixture of solvent red dyes or a composite black can be obtained by mixing several dyes. Suitable carrier materials can include paraffins, microcrystalline waxes, polyethylene waxes, ester waxes, fatty acids and other waxy materials, fatty amide containing materials, sulfonamide materials, resinous materials made from different natural sources (tall oil rosins and rosin esters, for example), and many synthetic resins, oligomers, polymers, and copolymers.
Ink sticks are used in a number of solid ink printers because they enable the ink to be formed with a particular configuration rather than the more generic and non-differentiated structure of pellets. Currently, solid ink sticks are typically manufactured with a formed tub and flow fill process. In this method, the component dyes and carrier composition are first compounded and then heated to a liquid state and poured into a tub having an interior shape corresponding to the desired finished ink stick shape. The result is an ink stick that, at room temperature, is typically a solid having a wax-like consistency. Colorant added to the ink composition can be a dye or pigment or combination. For simplification the term dye is used herein to describe the colorant added to an ink composition to provide color.
Solid ink sticks formed by the flow fill method may have aesthetic flaws because the top surface is not shaped by a surface and the melted ink may cool unevenly in the tub. In addition to aesthetic issues, the sticks may have wide range of dimensional variation that may adversely affect movement and orientation in the feed channels. Consequently, the feed channels are required to be made with structures that are tolerant of these relatively wide dimension ranges. The feed channels are also typically configured with sensors for monitoring the amount of solid ink in a channel in order to generate signals for notifying operators that additional solid ink should be loaded into a channel. The wider dimensional ranges of ink sticks accommodated by feed channels may make sensor placement or location more difficult or affect sensing functions. Additionally, significant differences in molten versus solid densities may cause ink sticks formed by the flow fill method to have internal stresses that result in breakage during handling and shipping. Cracks and internal air pockets may also develop during cooling of the ink in the tub and enable the sticks to absorb moisture from the environment. These issues are exacerbated when flow fill methods are used to make larger mass sticks.
Compression molding is an alternative method for forming solid ink sticks. In this method, solid particulate is poured into a mold and then a surface that fits the opening through which the solid ink particulate was poured is pressed against the particulate with sufficient force that the particulate melts and conforms to the pressure chamber formed by the surface and the mold. This method addresses many of the issues that may occur with fill-flow methods, but the compression molding method may fail to seal the outer surface or skin of the sticks uniformly. Thus, sticks made by this method may also allow moisture to be absorbed from the air.
Industry standard liquid injection molding methods have been accomplished with limited success. A small ink stick or one with a narrow cross section may be produced with such a method without incurring significant problems, such as deformation, cracks, internal stresses, air pockets, or damage to the sticks, provided that the dwell time for the liquid material in the mold cavity is sufficiently long that the liquid ink is permitted to solidify substantially. As sticks become more complex in shape and larger for a multitude of performance and user requirements, the standard molding processes fail to produce ink sticks that do not suffer from one or more of the above-identified problems. Additionally, the larger and more complex ink sticks tend to stick in the molds. Thus, while molding is desirable to obtain dimensional accuracy, shape complexity, and improved aesthetics, no current molding process appears capable of reaching these goals.